Advances in miniaturization of integrated circuits have led to the remarkable miniaturization of computer systems. Room-sized mainframe computers of the 1950s gave way to large, cabinet-sized mainframe and mini-computers of the 1960s and 1970s. The personal computers that emerged during the 1980s today provide, in a desk-top system, greater computing capacity than large mainframe or mini-computers from preceding decades. In the 1990s, personal computers have been further miniaturized to produce portable, convenient laptop computers powered by batteries. High-end laptop computers currently approach the performance of high-end desktop systems. The increase of battery capacity through technological innovation has not, however, kept pace with the increase in the density of integrated circuits and concomitant miniaturization of computer systems. Although newer active matrix display screens and low-resistance pin connection technologies have helped to lower the power consumption of laptop computers, and thereby extend the length of time during which a laptop computer can operate using the available battery capacity, the usefulness of laptop computers is limited by limitations in battery capacity.
Manufacturers have adopted a variety of strategies for conserving the use of electrical energy stored in the batteries of laptop computers. Newer laptop computers employ power management strategies in which unused components are detected and automatically powered down or suspended until they are again required for operation of the computer. For example, the display screen of modern laptop computers is automatically powered down after a period of quiescence. Similarly, the central processing unit ("CPU") of a modem laptop computer is powered down, or suspended, when the computer has not executed any application programs or processed any input or output activities for some period of time.
As with desktop personal computers, laptop computers are being used with increasing frequency not only for executing application programs, but also as a platform for viewing and listening to multimedia presentations and entertainment programs. The CD-ROM drive included with most laptop computers and desktop computers can be used, for example, to playback recorded music CDs through loud speakers attached to the laptop or desktop computer. Playback of recorded music CDs (audio CDs) is commonly implemented through software application programs executed by the CPU. In many current systems, the CPU remains in a powered-on state while the CD-ROM drive is being used for playback of an audio CD. Because the CPU consumes power at a high rate, use of a laptop computer for playback of recorded music CDs is quite limited by battery capacity. A large portion of the power consumed during playback of recorded music in these computer systems is dissipated as heat from the CPU performing largely unused instructions cycles. A need has therefore been recognized by manufacturers of laptop computers to more effectively manage power consumption during playback of an audio CD on a laptop computer when the CPU of the laptop computer is otherwise not being used to either execute application programs or to control the CD-ROM drive.